It is known to employ multiple hot runner valve gates to fill large mold cavities. It is also known to employ sophisticated automatic control for the opening and closing of the multiple valves in sequence in order to optimize the filling and packing of the large mold cavities and in response to cavity pressure sensor signals. The present invention provides a simple, inexpensive and easily utilized improvement particularly useful with such multiple hot runner valve gates for filling such large cavity molds.
U.S. Pat. No. 4,420,452 to van Dalen et al. teaches the sequential feeding of resin through a series of hot runner valves to fill a single large cavity mold. The valves are disclosed as being pneumatically, hydraulically or electrically opened and closed in any desired sequence using a process computer, although the details of how the valves are controlled and the design of the valves themselves are not shown. U.S. Pat. No. 5,556,582 to Kazmer teaches two hot runner valve gates, each with servo-hydraulic controlled valve stems that respond to a closed loop control system sensing melt pressure in the mold cavity for filling a single large mold cavity. During molding, the valves are adjusted based on information from the sensor. However, this automatic system is very expensive to build and requires a computer to be programmed to process sensing data in order to provide control signals to the servo controlled valves.
Other references teach various ways for mechanically adjusting the closing or opening position of hot runner valve stems in single or multi-cavity molds. U.S. Pat. No. 3,491,408 to Notkins teaches a manually adjustable threaded stop for setting opening position. U.S. Pat. No. 3,252,184 to Ninneman shows a hot runner injection orifice control with adjustable valve stem control for each nozzle feeding its own cavity using spring closing and fluid pressure opening against a preset stop. U.S. Pat. No. 3,561,062 to Goron teaches an injection molding nozzle with a flow-control mechanism within each nozzle employing a rotatable nozzle which can be progressively turned to regulate the flow of resin into the mold cavity. U.S. Pat. Nos. 5,067,893 and 5,141,696 to Osuna-Diaz show injection molding devices having actuation systems for operation of a shut-off valve stem movably mounted in a valve gate employing a worm/gear drive for controlling the valve stem position. U.S. Pat. No. 5,780,077 to von Holdt teaches a worm/gear drive for adjusting a nozzle opening that does not include a valve stem. U.S. Pat. No. 4,330,258 to Gellert shows a mechanical double acting mechanism for actuating valve stems in valve gated injection molding systems. U.S. Pat. No. 4,088,271 to Flygenring shows a still further embodiment for mechanically adjusting the valve stem position.
Individual control of multiple hot runner valve gates each supplying its own mold cavity are taught by U.S. Pat. 4,279,582 to Osuna-Diaz which shows a hydraulic system and U.S. Pat. No. 4,592,711 to Capy which teaches a worm/gear method for rotating the nozzle to block the supply channel flow in combination with a two position actuated valve stem for sequentially feeding multiple mold cavities.
None of the foregoing mechanical valve stem position control means contemplate a predetermined intermediate settable position for the valve stem wherein the rate of resin flow filling the mold cavity is altered by moving the valve stem to said predetermined intermediate settable position during filling, particularly to restrict the flow of melt through the valve gate. Such a system would be highly desirable.
Japanese Patent 62-41851 teaches a rack/gear driven method for driving a valve stem in a coinjection nozzle to one of three positions to select which of the two melt channels can fill the mold cavity. While this reference teaches an intermediate valve stem position, it is for the purpose of blocking or unblocking a second resin supply channel in a coinjection nozzle and it does not contemplate altering the flow rate of a single resin supply channel during the filling process.
It is, therefore, the principal object of the present invention to provide an improved injection method and apparatus employing a hot runner injection nozzle having a gate through which melt is injected into a mold cavity.
It is a further object of the present invention to provide a method and apparatus as aforesaid which permits the altering of a single melt supply channel during the mold cavity filling process.
It is a still further object of the present invention to provide a method and apparatus as aforesaid which is particularly useful with multiple hot runner valve gates to fill single large mold cavities.
Further objects and advantages of the present invention will appear hereinbelow.